docs: def com_google_fonts_check_glyf_unused_data(ttFont):
    """Is there any unused data at the end of the glyf table?"""
    try:
      expected_glyphs = len(ttFont.getGlyphOrder())
      actual_glyphs = len(ttFont['glyf'].glyphs)
      diff = actual_glyphs - expected_glyphs
  
      if diff < 0:
        yield FAIL, Message("unreachable-data",
                            ("Glyf table has unreachable data at the end of "
                             " the table. Expected glyf table length {}"
                             " (from loca table), got length"
                             " {} (difference: {})").format(
                                 expected_glyphs, actual_glyphs, diff))
      elif not diff:  # negative diff -> exception below
        yield PASS, "There is no unused data at the end of the glyf table."
      else:
        raise Exception("Bug: fontTools did not raise an expected exception.")
    except fontTools.ttLib.TTLibError as error:
      if "not enough 'glyf' table data" in format(error):
        yield FAIL, Message("missing-data",
                            ("Loca table references data beyond"
                             " the end of the glyf table."
                             " Expected glyf table length {}"
                             " (from loca table).").format(expected_glyphs))
      else:
        raise Exception("Bug: Unexpected fontTools exception.")